Impact of pendant substituents on post-polymerization functionalization and electronic properties in stereoregular non-conjugated pendant electroactive polymers

Abstract

Recent reports on non-conjugated pendant electroactive polymers (NCPEPs) have demonstrated the significance of altering structural variables specifically the stereoregularity, the nature of the pendant group and the length of the spacer connecting that group to the backbone for tuning of their optoelectronic properties. The only synthetic approach that allows for selectively studying the effects of tuning these variables without additional superimposed effects of varied molecular weights and tacticities is the post-polymerization functionalization methodology in which parent polymers are synthesized first and then functionalized with the respective pendant groups and spacers. However, specifically for tuning of the pendant group itself, the scope of such post-polymerization functionalization methods remains largely underexplored. Here, the compatibility of the established photochemical thiol-ene post-polymerization method with various pendant groups is investigated for functionalization of stereoregular and stereorandom poly(allyl methacrylates) made via anionic polymerization using an organolithium initiator. Carbazole and a family of four 3,6-disubstituted carbazoles with phenyl, methoxy, nitrile and t-butyl substituents were investigated as the respective pendant groups. With the phenyl, methoxy and nitrile substituted pendant groups limitations of the scope of the thiol-ene methodology due to limited solubility and vulnerability to photochemical side reactions could be demonstrated. In contrast, t-butyl substituents did not impede the post-polymerization functionalization. The corresponding functionalized NCPEPs were characterized and effects of substitution of the carbazole pendant group with t-butyl groups on the optoelectronic properties of the polymers are discussed. Overall, this work demonstrates critical limitations of the thiol-ene functionalization method as well as their origin when applied to differently substituted pendant groups.